Filter devices of this type are readily available on the market in a plurality of constructions and versions. Such filter devices are used mainly to filter out fouling in fluids, such as hydraulic. Fouling of the hydraulic oil occurs in the installation or at the start-up of the respective hydraulic system. In addition to this initial fouling, fouling can occur during operation, for example, by penetration of dirt at the hydraulic tank as a result of inadequate tank ventilation, pipe penetrations, piston rod seals, and the like. Fouling can occur within the fluid stored in the hydraulic tank, especially in the hydraulic systems of heavy machinery such as earth moving machines, excavators, or the like. Furthermore, in these types of applications of the filter device, effecting filtration directly in the region of the hydraulic tank, for example, by installing the filter device directly in the tank, can be useful.
DE 10 7007 056 362 A1 discloses a filter device, especially in the form of a return intake filter, having at least one filter housing in which at least one filter element defines one longitudinal axis and can be accommodated. At least two valve units, especially in the form of a bypass valve and a back pressure valve, are located in an arrangement concentric to and along the longitudinal axis of the respective filter.
DE 10 2006 011 844 B4 discloses a filter element with a filter bowl that borders an interior, with a bottom part having a flow passage, with a filter medium located in the interior of the filter bowl, and with a valve body of a valve apparatus. The valve body can be actuated by the fluid pressure on the fluid passage of the bottom part, and has a screen-like, flexible closing jacket. In the opened-up state, the closing jacket blocks the fluid passage, is moved by the fluid pressure in the direction to its closed position, and clears the fluid passage.
In these two aforementioned filter solutions, the respective valve arrangements for the filter element installed in the filter housing are actuated accordingly in their respectively provided operating position and by the respectively prevailing fluid pressure, especially of the fluid to be filtered. Under the conditions of use prevailing in the operation of the filter device in construction machinery or other machinery operated in the open, due to the higher fouling rates that arise, frequent changing of the filter element must be done. In the course of handling the used, i.e., fouled, filter elements, in these known solutions, the risk exists that contamination both of the system, i.e., especially of the filter housing and the tank, and also of the environment, will occur.
DE 10 2005 001 828 A1 discloses a fitting forming a fluid-conducting connection to a plastic tank, in particular a tank for accommodating a fluid, specifically a hydraulic fluid. The tank has a connection part in the form of a hollow body with a jacket that extends along one longitudinal axis of the hollow body between its ends. The hollow body is embedded in the plastic of the wall of the tank such that one open end of the hollow body on the edge of an opening of the tank and at least one partial region of the jacket of the hollow body are surrounded by the plastic of the wall of the tank. A filter element can be reliably integrated in a tank by this fitting. However, in a replacement of the used filter element by a new element in turn it cannot be precluded that the above-described fouling problems will occur.